This paper describes the challenges faced when completing wells in the Mishrif formation of Southern Iraq, where well control concerns increase post acid stimulation of the reservoir due to the unpredictability of the formation's behavior.
One of the biggest challenges faced when drilling and completing in this formation is to manage a natural hydraulic balance of the reservoir to avoid the well switching from losses to kicks without warning. While this challenge is being addressed by carefully selecting drilling and completion fluids of specific densities, it has not been fully mitigated as wells have shown signs of switching state arbitrarily specifically post acid stimulation operations. In light of this challenge a completion design was proposed that incorporated a downhole bi-directional barrier valve which would ensure that the well bore would be secure upon installation of the lower completion. It was envisaged that this technology would help overcome any dynamic changes of the reservoir that may lead either to fluid loss, risking damage to the reservoir or kicks risking a catastrophic blow out.
A typical production well architecture in the Mishrif formation of the West Qurna-2 field would consist of 9-5/8″ production casing to surface and an 8-1/2″ Open Hole section that would be completed with either 7″ slotted or perforated liner. Well trajectories could vary from vertical to a maximum deviation of 60 degrees in most cases. The proposed design was to complete a few of the early phase wells using 9-5/8" × 5-1/2" mechanical ball valves incorporated into the lower completion which would therefore serve as a bi - directional barrier once installed and shifted closed.
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